The demand for access to digital communications networks, such as the Internet, is directly related to the speed or rate at which such networks can transfer data. Higher data transfer rates provide a foundation for increased communication efficiency and new types of communication applications or services. These, in turn, fuel demand for more widespread network access and still-higher data transfer rates.
Conventional analog modems currently provide a maximum data transfer rate of 56 kilobits per second (kbps). Other technologies, such as cable modems, can offer significantly improved performance, but typically require changes in a telecommunication network's underlying architecture. Such changes may necessitate large network infrastructure investments to meet user demand for network accessibility.
Digital Subscriber Line (DSL) technology provides increased communications bandwidth while using existing twisted-pair copper lines that are prevalent throughout much of the world. DSL delivers a basic data transfer rate of 128 kbps. High speed DSL, or HDSL, can deliver a data transfer rate of 1.544 megabits per second (Mbps) in North America, and 2.048 Mbps elsewhere. Asymmetric DSL, or ADSL, can deliver data rates ranging from 1.5 to 9.0 Mbps on a downstream or receiving path, and 16 to 800 kbps on an upstream or sending path. Taken together, varying DSL technologies are referred to as xDSL.
FIG. 1 is a block diagram of a conventional xDSL communications network organization. In FIG. 1, a set of Customer Premises Equipment (CPE) units is coupled to a Main Distribution Frame (MDF). Each CPE unit comprises an XDSL modem, and is located at a customer site. The MDF is coupled to an access matrix, which itself is coupled to a DSL Access Multiplexer (DSLAM) and a test unit. Each of the MDF, the access matrix, the test unit, and the DSLAM reside at an xDSL service provider's site. The DSLAM is also coupled to a network gateway or hub, which in turn is coupled to a high-speed transmission line or backbone that connects to an external network. Finally, the access matrix, the DSLAM, and the test unit are each coupled to a control computer.
The high-speed backbone is characterized by a data transfer rate much greater than that associated with any given CPE unit. Taken together, the DSLAM, the access matrix, and the MDF provide a signal exchange interface between the high-speed backbone and the CPE units. The DSLAM includes a set of XDSL modems and signal multiplexing circuitry, while the access matrix includes computer-controlled switching circuitry.
Each CPE unit is coupled to the MDF via a network of twisted pair wiring. The signal transfer pathway between any given CPE unit and the MDF is commonly referred to as a “local loop.” A local loop's maximum data transfer rate is dependent upon its electrical characteristics, as readily understood by those skilled in the art. Due to variations in signal path length, environmental conditions, and interconnection history, any given local loop's electrical characteristics may significantly differ from those of another local loop. Moreover, a local loop's electrical characteristics may change over time due to variations in twisted pair line conditions. As a result, the ability to determine accurately local loop electrical characteristics is critical to the installation and maintenance of xDSL connections.
The test unit comprises hardware and software that facilitates local loop electrical characterization. The test unit provides capabilities such as those described in U.S. patent application Ser. No. 09/215,421, entitled “Telecommunications Transmission Test Set,” filed on Dec. 18, 1998; and U.S. patent application Ser. No. 09/295,857, entitled “Detection of Bridge Tap Using Frequency Domain Analysis,” filed on Apr. 21, 1999.
The organization of the DSLAM, the access matrix, and the test unit as shown in FIG. 1 is undesirably space and cost inefficient. In many prior art configurations, the test unit is roughly comparable in size to the DSLAM itself. What is needed is a different type of configuration that is highly space and cost efficient.